1. Field of the Invention
The present invention relates to an image bearing member.
2. Discussion of the Background
In an image forming apparatus using electrophotography, images are formed by processes of charging, irradiation, development, transfer etc. applied to an image bearing member, for example, a photoreceptor.
Corona products produced in the charging process that remain on the surface of the image bearing member, and toner or its component remaining on the surface of the image bearing member after the transfer process, are removed by a cleaning process.
For the cleaning process, a cleaning system having a cleaning blade such as a rubber blade is typically used because such a cleaning blade has a simple and cost-saving configuration with good cleaning properties. However, since the cleaning blade is pressed against the image bearing member to remove residual material on the surface thereof, the cleaning blade is under heavy stress including mechanical stress caused by friction between the surface of the image bearing member and the cleaning blade. This leads to attrition of the cleaning blade and the surface layer of the image bearing member particularly in the case of an organic photoconductor, which shortens the working life of both the cleaning blade and the organic photoconductor.
In addition, the toner used in image formation is reduced in particulate size to satisfy demand for improved image quality. In the case of an image forming apparatus using a toner having a small particle diameter, the proportion of residual toner that slips through between the edge portion of the cleaning blade and the surface of the image bearing member tends to increase. This is particularly true when dimensional accuracy and/or assembly accuracy are not sufficient or the cleaning blade partially vibrates, which degrades the quality of output images.
To deal with this problem, for example, a method is employed in which a lubricant (i.e., protective agent) is powdered by rotating an applicator brush that contacts the lubricant (typically in solid form) and supplied to an image bearing member, and a film of the lubricant is formed thereon by the cleaning blade.
Because of the lubricant present between the image bearing member and the cleaning blade, the cleaning blade and the surface of the image bearing member are protected. Therefore, abrasion of the image bearing member and deterioration of the blade caused by friction between the blade and the image bearing member is reduced. In addition, the deterioration of the image bearing member caused by discharging energy when the image bearing member is discharged is reduced.
In addition, the protective agent applied to the surface of an image bearing member increases the lubricant property thereof, thereby reducing the partial vibration of the cleaning blade. Therefore, the amount of toner that slips through beneath the cleaning blade in the cleaning process is reduced.
However, in the above-described method, the lubricant is supplied to the image bearing member while the image bearing member is in rotation for image formation. Therefore, unless a film of the lubricant is preliminarily applied to the surface of the image bearing member prior to image formation, the image bearing member has no lubricant on its surface before image formation. That is, the lubricant property between the image bearing member and the cleaning blade is poor before image formation starts, thereby degrading both the blade and the image bearing member.
In addition, color image forming apparatuses have come into wide use of late and market demand for quality images is increasing. Thus, the most common charging system currently employed uses a charging roller applying an AC voltage in which an AC voltage is overlapped with a DC voltage to the surface of the image bearing member. Furthermore, an AC charging system using a charging roller satisfies the need for size reduction, produces smaller amounts of oxidized gases such as ozone and NOx, and naturally is expected to be widely used in the future.
However, a drawback of the above-described AC charging system is that the image bearing member is charged with repetitive positive and negative discharging several hundreds to several thousands of times per second depending on frequency when the AC charging system is used. Thus, the image bearing member is easily and heavily damaged in the AC charging system in comparison with a DC charging system in which an image bearing member is charged with positive discharging only once while the image bearing member passes through the charging device. Therefore, protecting the image bearing member from the damage caused by charging is demanded of the AC charging system.
For the foregoing reason, there is a strong need for an improved cleaning blade effective to protect the image bearing member from AC charging, apply a large amount of a lubricant to an image bearing member, and remove toner having a small particle diameter. However, taken together, these requirements, when satisfied, lead to acceleration of deterioration of the cleaning blade.
In addition, if the brush is strongly pressed against a protective agent to supply it in a large amount, the protective agent having a large particle diameter is supplied to an image bearing member. Therefore, the protective agent easily slips through a cleaning blade and the protective agent tends to be not uniformly covered by the protective agent.
In addition, toner that has slipped through the cleaning blade and a lubricant such as metal soap scatter and easily attach to the charging roller, thereby causing bad charging. Therefore, protecting the charging roller from contamination also creates a problem.
Typically, the working life of the image bearing member is long, but the charging roller and the cleaning blade tend wear out relatively quickly and are replaced when they deteriorate. However, in terms of concerns for the environment, there is a strong need for prolongation of the working life of each member such as the charging roller, the cleaning blade, and the image bearing member. Therefore, technologies are demanded that prevent deterioration and contamination of each of these members.
Thus, for example, use of metal soap as the protective agent leads to metal soap powder being supplied to an image bearing member, passing through the cleaning blade, scattering to the charging roller and attaching thereto, causing poor charging. However, mixing an inorganic lubricant such as boron nitride (BN) and a metal soap instead of just the metal soap alone is known to be effective to solve this problem.
A lubricant mixture in which an inorganic lubricant is mixed with metal soap and solidified into a bar can be used instead of the typical lubricant (i.e., zinc stearate).
For example, JOP 2008-134467-A describes using a mixture in which boron nitride (BN) is blended with metal soap as the protective gent instead of metal soap. In this case, mica or boron nitride is blended with metal soap (zinc stearate) to reduce scattering of the metal soap to the charging roller and abrasion of the cleaning blade for an extended period of time.
However, since boron nitride (BN) is extremely expensive, there is a trade-off between the cost and the effect when using boron nitride.
For these reasons, the present inventors recognize that a need exists for an image bearing member and an image forming apparatus that produce quality images for an extended period of time, and provides an extremely long working life with less frequent replacement to other members such as the charging roller, the cleaning blade, and the protective agent applicator blade arranged around the image bearing member.